Three groups of investigators including our own independently demonstrated a cytopathic effect transmissible in cell culture in intestinal tissue filtrates derived from most patients with inflammatory bowel disease (IBD). The effect appears to be due to an RNA virus or viruses. Most recently viral particles visible under EM have been isolated from infected cultures by cesium chloride density gradient centrifugation of concentrated medium pour-off in our laboratory. In addition, we have recently identified circulating interferon in many patients with active IBD. The present proposal in which various aspects of immunity to intestinally-derived viral isolates will be studied offers an essential step in attempting to satisfy Koch's postulates for the agents isolated from IBD tissues. These studies will also examine further the role of lymphocyte-mediated tissue damage in IBD and in particular, the potential significance of viral infection in these processes. Initially, we propose an investigation of lymphocyte-mediated cytotoxicity against both non-specific target cells and targets infected with the putative viral agents. Effectors will include lymphoid cells from peripheral blood and mesenteric lymph nodes. At the same time, a major effort will be mounted to obtain pools of viruses by concentration and banding of medium pour-offs from roller bottle cultures infected with the IBD- and disease control-derived agents. The resulting isolates will undergo further virologic characterization and will serve as reagents for the development of antisera by the production of monoclonal antibody secreting hybridomas and by conventional hyperimmunization techniques. The antisera will then be utilized in a direct solid phase RIA procedure to investigate whether the various isolates are antigenically distinct. These antisera will also be used in immunofluorescent tests of infected cell cultures in efforts to identify the presence of cell surface expression of viral antigens. Subsequent studies will explore the application of these antisera and procedures to the development of serum antibody assays to these agents and the detection of viral antigen in intestinal tissue samples.